Changing the chemical and physical properties of high valent heterobimetallic bis-(μ-oxido) Cu–Ni complexes by ligand effects

Abstract

Two new heterobimetallic [LNiO₂Cu(RPY2)]⁺ (RPY2 = N-substituted bis 2-pyridyl(ethylamine) ligands with R = indane, 3a or R = Me, 3b) complexes have been spectroscopically trapped at low temperatures. They were prepared by reacting the mononuclear side-on LNi^II superoxo precursor bearing a β-diketiminate ligand (L = [HC-(CMeNC₆H₃(iPr)₂)₂]) with the Cu(I) complexes. In contrast to the oxo groups in known high-valent [M₂(μ-O)₂]ⁿ⁺ (M = Fe, Co, Ni, Cu) cores that display electrophilic reactivities, 3a and 3b display rather nucleophilic oxo cores active in aldehyde deformylation reactions. However, the spectroscopic and reactivity properties of 3a/3b are found to be distinct relative to that of the previously reported [LNiO₂Cu(MeAN)]⁺ complex containing a more basic (nucleophilic) N,N,N′,N′,N′-pentamethyl-dipropylenetriamine (MeAN) ligand at the copper centre. The geometry and electronic properties of the copper ligands affect the electron density of the oxygen atoms of the heterodinuclear {Ni(μ-O)₂} core and 3a/3b undergo slower nucleophilic and faster electrophilic reactions than the previously reported [LNiO₂Cu(MeAN)]⁺ intermediate. The present study therefore demonstrates the tuning of the electrophilicity/nucleophilicity of the oxygen atoms of the heterobimetallic [Ni(μ-O)₂Cu]²⁺ cores by controlling the electron donation from the ancillary ligands, and underlines the significance of subtle electronic changes in the physical and chemical properties of the biologically relevant heterobimetallic metal–dioxygen intermediates.